The invention generally relates to safety protective coatings for glass containers to resist breakage and shattering. More particularly, the invention is directed to providing a safety coating for a coffee decanter that is subjected to intermittent heating.
Serving heated beverages from decanters, such as used for hot coffee, requires care to be taken so that rough treatment and breakage of the decanter do not occur. While the prevention of injuries from broken glass and hot coffee is a normal concern of consumers for use in the home, the problems are multiplied when coffee, or other hot beverages, are served to the public in restaurants or handled in busy kitchens by employees. Even great care and warning labels sometimes do not avoid accidental breakage. Coffee decanters used in restaurant facilities are subjected to excessively rough handling and oftentimes are knocked against one another, as well as against metal countertop edges and other pieces of restaurant equipment. Not only can injury result from skin contact with the hot liquid but also from the shards of glass that may be strewn about when a decanter is shattered.
Coffee decanters are required to have a relatively thin construction to avoid cracking from drastic expansion differences at the interior versus the exterior because they are subjected to quick changes in temperature from ambient conditions to holding heated coffee up to about 205.degree. F. Should a coffee decanter be made with thick walls, heat fracturing might occur due to differences in surface expansion inside to outside. Furthermore, decanters are often placed upon warming plates that may have surface or heating element temperatures exceeding 500.degree. F. In the event that an inattentive employee allows a decanter to "boil dry", temperatures in excess of 500.degree. F. may be reached at the lower wall surfaces of the decanter. Accordingly, a protective coating must be able to withstand quick temperature changes and elevated temperatures in addition to providing for the break and shatter resistance that has long been sought in the industry.
By necessity, coffee decanters, and other hot beverage holding containers, have relatively narrow open neck portions to minimize heat loss in order to keep the beverages warm and to provide for easy pouring. A common bulbous bowl shpae has long been used in the industry. This design also places the center of the gravity very low and makes it less likely that spillling could occur while carrying the decanter from a coffee warmer to, for example, the table side in a restaurant where the coffee is to be poured by the waiter into a cup. The thin, shell-like wall configuration also allows for even and rapid heat conduction to maintain the beverage at an appropriate temperature when rested upon a warming plate between servings.
The prior art has utilized coatings to protect pop bottles from breakage such as disclosed in U.S. Pat. No. 3,825,142 to Campagna and U.S. Pat. No. 3,859,117 to Erchak et al. However, the problems encountered with glass decanters that are subjected to intermittent heating and drastic temperature changes are not addressed in the prior art.
Additional prior art teachings of protective coatings for glass are disclosed in U.S. Pat. No. 4,161,556 to Lenard et al., U.S. Pat. No. 4,220,682 to Macedo et al., U.S. Pat. No. 4,268,554 to Gras, and U.S. Pat. No. 4,289,816 to Fogelberg et al. Another teaching providing for coating glass surfaces, such as soda bottles or lightbulbs, is shown in U.S. Pat. No. 3,529,035 to Lamoreaux. In the Lamoreaux invention, a silicone elastomeric coating is used to prevent shattering when the glass is broken. The Lamoreaux patent, however, does not show or consider providing a protective coating that may be used on liquid-holding glass containers which are subjected to intermittent heating and cooling during use, or that is capable of resisting shattering after a container has been "boiled dry" on a heating plate and remains on the plate for a substantial period of time.
Many overlapping concerns with container breakage are found in other areas of use, such as in chemical laboratories where glass containers similar to coffee decanters are used. A long-sought advance in the art of safety protection in the laboratory environment has been to provide for a coating material for glassware containers that resists breakage and substantially eliminates shattering should a blow severe enough to cause breakage occur. These concerns must also be addressed in connection with keeping the coating viable even after experiencing temperature fluctuations like those encountered in coffee brewing procedures.
In the field of glass containers for heated liquids a long-sought goal has been to achieve a safety coating which will also serve as a tough, elastomeric envelope or pouch to confine shards of glass in the event the glass container is broken. While it is desirable that the elastomeric envelope not leak in the event of breakage of the glass container, minor leakage may be tolerated as long as fragments of glass are confined and spewing of heated liquid is avoided in order to prevent personal injury.
Of particlar concern to the restaurant and food service industry is that a protective and safety coating should meet federal Food and Drug Administration food grade material standards. Further, it is important that the safety coating be transparent so that the contents of the decanter may be readily observed by the restaurant employee in order to monitor the amount remaining and to distinguish one beverage from another. The safety coating should not yellow or otherwise become less transparent with age, and it must be non-flammable. Also, the safety coating must not age harden to the point that it becomes brittle and subject to shattering.
The answer to the forgoing problems is not simply achieved by merely creating a shock absorber layer, such as provided by plastic films, foams, or epoxy resins coatings of the thermoset variety as shown in U.S. Pat. No. 4,351,573 to Bradley et al. While a certain degree of thermal shock resistance is provided by these coating materials, the prior art uses have not included applications to "hot-type" containers.
With the need for glass containers that are usable for microwave cooking, it has sometimes been desirable that a coating, such as an epoxy resin, have the property of rupturing, and therefore being frangible. This property is critical for certain types of glass food containers, along with thermal resistance for microwave cooking, because any rupture of the glass wall necessarily ruptures the frangible coating so that leakage may be discerned in order to avoid contamination. Contrarily, for hot beverage containers used in the food services industry, or in the consumer's home kitchen, an important concern has been to prevent the coating from rupturing with the decanter. Teachings of frangible coatings to permit detection of leakage and contamination are otherwise concerned with the problems in containerized foods for sale on the grocery store shelf and not with the problems of holding or serving hot liquid in containers. As a result, this form of prior art protective glass coating is inherently inapplicable to the problems our present invention solves.
A shatter-resistant plastic coating for glass containers used to hold liquids while being subjected to intermittent heating and cooling, has been lacking in the prior art. Further, the art has failed to provide plastic coated glass containers for liquids that resist shattering after having been boiled dry on a warming plate, or heating element, and left for a substantial period of time. Decanters for heated beverages, such as used for coffee and tea, employing silicone rubber coatings to achieve shatter-resistance, have not been known in the glass container industry.